Pull up resistor is a well known concept.

Probably, after reading on this too much, I totally lost it and confused - how it works on a basic level

**When we place a certain pull up resistor (R), how the actual Voltage and Current are being determined ?**

The well known formula \( U=I*R \) has 2 unknown variables (U & I).

Please help understand on the following example:

Assume we have the following setup

The TTL IC has the following INPUT definitions:

While calculating, I can pick different values of V[in] and find the relevant I[in]....but how actually the setup will behave ?

(Vcc=5V; R=10K)

Case No | V[in](picked by me for the following calculations) | Vr (voltage dropped by R= Vcc-Vin) | I[in] (=Vr / R) |
---|---|---|---|

1 | 4.6V | 0.4V | 40uA |

2 | 4.0V | 1V | 100uA |

3 | 0.2V | 4.8V | 480uA |

*For convenience, f*rom SN74LS04 datasheet: